title: Renal inner medullary prostaglandin synthesis. A calcium-calmodulin-dependent process suppressed by urea.
abstract: Previous studies have demonstrated that hyperosmolar NaCl and mannitol stimulate immunoreactive prostaglandin E (iPGE) production by slices of inner medulla (IM), whereas urea inhibits this process. In the present study, the roles of Ca2+ and calmodulin in the control of PGE synthesis in IM and the basis for the differential actions of solutes were examined. A23187 increased [14C]arachidonate (AA) release and iPGE accumulation in the presence but not in the absence of media Ca2+ whereas stimulation by hypertonic NaCl or mannitol was well expressed with Ca2+ or in Ca2+-free buffer containing 2 mM EGTA. Hypertonic urea and trifluoperazine (TFP), an inhibitor of actions of the Ca2+-CaM complex, suppressed increases in [14C]AA release and iPGE induced by A23187, NaCl, or mannitol. By contrast, increases in iPGE in response to exogenous AA were not altered by urea or TFP. Ca2+ (25-100 microM) increased acyl hydrolase (AH) activity in EGTA washed (4 degrees C) 100,000 g particulate fractions of IM threefold, thereby restoring AH activity to the higher basal values of particulate fractions not washed with EGTA. This action of Ca2+ was blocked by hypertonic urea of TFP, whereas AH activity was not influenced by NaCl or mannitol in the presence or absence of Ca2+. In contrast to their effects on AH activity, hypertonic urea and TFP did not alter conversion of AA to PGE2, PGF2 alpha, or PGD2 by IM microsomal fractions. Ca2+-induced increases in particulate AH were blunted after partial depletion of endogenous CaM-like activity. Ca2+ action was restored by addition of purified exogenous CaM, but not by addition of other small acidic proteins, including troponin C. The findings support a role for CaM in the regulation of PGE synthesis in the IM at the level of Ca2+-responsive AH activity. They further imply that urea suppresses PGE synthesis in IM through inhibition of AH and a reduction in the availability of endogenous AA for conversion to PGE.
mesh_terms: D000581:Amidohydrolases / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D005260:Female; D066298:In Vitro Techniques; D007679:Kidney Medulla / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D008353:Mannitol / Q000494:pharmacology; D011453:Prostaglandins / Q000096:biosynthesis*; D011458:Prostaglandins E / Q000096:biosynthesis; D051381:Rats; D012965:Sodium Chloride / Q000494:pharmacology; D014508:Urea / Q000494:pharmacology
chemical_list: D001095:Arachidonic Acids; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D011453:Prostaglandins; D011458:Prostaglandins E; D016718:Arachidonic Acid; D008353:Mannitol; D012965:Sodium Chloride; D014508:Urea; D000581:Amidohydrolases; C019665:amidase; D008274:Magnesium; D002118:Calcium